obsessive behaviour

I wrote a few months back about "hunting instinct" kicking in as my baby saw a cat in a front garden ONCE and has to now look in every front garden. He is still doing this even though he has not seen a cat there since. How long a memory have they got!. Now because he saw a fox at the bottom of our communial garden whenever I let him out he has to run to the end of the garden first to see if the fox is still there before he will get on with the task in hand "Peeing before bedtime". He is driving me mad with his obsessions. You would think after a few weeks of the cat and fox not being where they were before he would get bored with the idea.